The key words are "interbreed successfully"; tigons and ligers generally are sterile and short-lived -- an evolutionary dead end.

In other words, the species is a population adapted to a certain niche, and if the members of different species could interbreed with each other, too much genetic variability would occur, reducing the success of the adaptation.

Another unifying factor is the rule of natural selection, which continues to act on species that have adapted to an environmental niche.

In this system all populations which are capable of interbreeding with each other and producing fertile offspring, and which do interbreed with each other in their natural state, are considered to be members of the same species, regardless how great their differences or how distant their relationship.

Perhaps only a minority of individuals in any given generation interbreed with other races under conditions of extensive contact, but over the course of generations all populations do, as the cumulative effect of a minority in each generation adds up to a majority -- and eventually a total population -- over a span of generations.

The distinctive racial characteristics of one or both of the parents are either negated or diminished as their racially unique, and therefore mutually incompatible, ensembles of genes are disrupted or diluted.

Supreme interbreed beef judge Bennett Jenkins’s impassive expression kept everyone guessing until he slapped the rump of Miss MRL, the Canadian bred Simmental dry cow exhibited by Roger Birch on behalf of himself and her two other owners.

The fixed effects were contemporary group, sex-of-calf H age-of-dam H breed-group-of-dam interaction, and group regression effects due to intra- and interbreed additive direct, intra (as a deviation from B) and interbreed additive maternal, and interbreed intralocus nonadditive direct and maternal.

The MREMLEM estimates of the intra- and interbreed additive, and interbreed nonadditive genetic covariances are shown in Table 1, whereas Table 2 contains the estimates of intra- and interbreed environmental covariances.

Interbreed AB Estimates of covariances were within acceptable ranges, except for the additive interbreed maternal variance for WW, which appeared to have been grossly overestimated.

Define interbreed - Definition of interbreed from Free-Online-Dictionary.org(Site not responding. Last check: 2007-11-04)

www.geocities.com In effect, then, creationists define a "kind" as (1) a group of organisms which do interbreed, or (2) a group of organisms which don't interbreed but which are similar in basic body plans--and then...

of populations that actually or potentially interbreed in nature, not according to similarity of appearance.

population is spread continuously across its range, and all the organisms in it freely interbreed.

We would also expect that similar species existing close to each other along that line would be able to interbreed or hybridize to a certain extent.

I realize this is hard to visualize through a podcast, but try to imagine a circle drawn with the letters A through E written clockwise along the circle.

If each of these letters represents a different subspecies, then A can interbreed with B, B can interbreed with C, C can interbreed with D, and D can interbreed with E. So far, this group of subspecies would be considered one big species, since in totality they can interbreed.

evolution-101.blogspot.com /2006/02/what-is-species.html (1555 words)

To Interbreed, As Races(Site not responding. Last check: 2007-11-04)

This 'balance' humans possess is also why humans can generally interbreed with most other races.

...contact that they can still interbreed, though it's only the oldest of elven sages who still remembers the ancient origins of the two races.

When a few individuals of two radically different races interbreed in an area of isolation and under primitive conditions, their progeny...

The answer to this one is a pretty clear "No"; chimps and humans have different numbers of chromosomes (humans have 23 pairs, chimps 24), which almost (but not completely) means any hypothetical offspring would be sterile.

Since the most commonly used definition of "species" requires that members of the same speciesinterbreed to produce fertile offspring, this means humans and chimps are not the same species.

Humans and chimps diverged at roughly the same time as did horses and donkeys (between 5 and 10 million years ago), and very roughly they are about as similar, genetically, as are horses and donkeys.

As somebody declared at ARN (Neil A. Wells), the animals able to interbreed can be considered as compatible software, and I must add that in order for that to be so it is necessary the complementarity of their genes (their ability to match).

You’re saying he means that the ability to interbreed and produce fertile offspring is the definition of a species.

Biologists would agree that the different finches are more likely to interbreed with eachother than is one finch to interbreed with a frog because they are genetically similar (chromosome count, introns, exons, etc).

teleological.org /WPblog/?p=165 (4692 words)

Interbreeding Between Species(Site not responding. Last check: 2007-11-04)

So, nearly everybody is in agreement that erectus could interbreed with sapiens: multiregionalists, afrocentrists, and even me. Note, however, that some people also say erectus was a distinct taxon.

I contend that view is confirmed by the genetic evidence cited in Age and Origin of the Human Species, Plural Lineages in the Human mtDNA Genome, and Australian Ancestry: Implications for the Origin of H. sapiens sapiens.

Thus, it isn’t clear (from the ape evidence) that even chromosomal rearrangements would have rendered the different types of Homo infertile, but it is clear that there were fewer such events, which even might have caused reproductive isolation, than there are recognized taxons of Homo.

In population genetics, a cline is a gradual change of a character or feature (phenotype) in a species over a geographical area.

A ring species is a special kind of cline where the geographical distribution in question is circular in shape, so that the two ends of the cline overlap with one another, giving two adjacent populations that rarely interbreed due to the cumulative effect of the many changes in phenotype along the cline.

The populations elsewhere along the cline interbreed with their geographically adjacent populations as in a standard cline.

Along with four first prizes and one second, her imported three shear ewe, Barda v-d Hoge Tornne won the Beltex championship and then went on to win the interbreed sheep award and was one of the interbreed pairs championship winners along with a home-bred hoggett ewe Artnagullion Ermontrude which has also had a successful season.

The pair were reserve in the interbreed group of three at Omagh Show with stock tup, the imported aged ram Bingo dal Cour, bought at the Carlisle 2000 sale.

Also at Balmoral her home-bred hogget ewe was placed fourth in the interbreed pairs contest along with a home-bred shearling tup from Mervyn Currie.

A ring species is a situation in which two populations which do not interbreed are living in the same region and connected by a geographic ring of populations that can interbreed.

Consider a species that is geographically distributed in a straight line from east to west across America: it is possible that the forms in the east and west are so different that they could not interbreed.

If they do not interbreed then the geographic distribution of the species will be in the shape of a ring, and they will be 'ring species': the extreme forms do not interbreed in the region of overlap.

www.blackwellpublishing.com /ridley/a-z/Ring_species.asp (244 words)

Do house cats interbreed(Site not responding. Last check: 2007-11-04)

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As reflected in the nomenclature, dogs are descended from the wolf and are able to interbreed with wolves.

The Coyote (canis latrans, or "prairie wolf") also interbreeds with dogs, and was interbred with dog by Plains Indians to produce some of their breeds.

Yellow jackals have 74 chromosomes and don't interbreed well with dogs, and other wild canids such as the bush dog, the maned wolf, and the fox, have different chromosome sets and cannot interbreed with dogs at all, so they played no part in the dog ancestry.

But under a theory called reticulate evolution, interbreeding can occur between closely related species, which means the evolutionary tree can sometimes look like a web (reticulate comes from the Latin word for net).

The most common cause of speciation is that animals from a single species become separated geographically.

Because they are no longer able to interbreed, they evolve along different paths.

www.amnh.org /learn/pd/genetics/profiles/cenglbrecht.html (459 words)

untitled(Site not responding. Last check: 2007-11-04)

A pair of moth species that could interbreed except that the female's mating pheromones are not attractive to the males of the othere species?

Two flowering plants that could interbreed except that one has a deep flower tube and is pollinated by hummingbirds while the other has a short, narrow flower tube andis pollinated by honeybees?

Species A and Species B occasionally interbreed and produce vigorous,fertile, offspring.

We know with certainty that all our existing breeds of dogs can interbreed; and also that the Dog will interbreed with the wolf and the jackal, although the exact extent of the fertility between the wolf and Dogs breed has not been determined...

It is like presenting you with the bones of a fossilized Chihuahua-like dog at the side of a living mastiff and then concluding that the mastiff "evolved" from the fossilized Chihuahua one...

Any varieties of dogs are able to interbreed producing fertile offspring, as well as with wolves, red wolves, jackals, coyotes, dingoes, etc., so all of them are only varieties of the same kind of organism in disregard of how 'speciation' is attempting 'to sell them by mususe' to deceive the unawares...

However, since the blue and white birds nest together and interbreed, taxonomists have determined that the blue goose is simply a color phase of the snow goose.

The two races interbreed and intermediate individuals are common in the zone of overlap.

In the US there are several populations of these feral swine, from the lowlands of South Carolina and Florida to the mountains of North Carolina to the "razorbacks" of Arkansas, to the wild pigs of Texas (and I do not speak of Javelina) and California.